New study is the first to examine the relationship between oxygen, temperature and metabolic demands of certain marine animals.
Not all marine animals find that warming oceans is shrinking their viable habitats. About 20 years ago, jumbo squid, historically found at more tropical latitudes, appeared in record numbers off the coast of central California. thesis voracious eaters subsisted on hake, rockfish and other commercially important species, disrupting the local supply chain. At the time, there was no clear reason why this happened, as scientists suggested the squid arrived due to a combination of climate change and overfishing.
Now a research team led by Brad Seibel Professor and expert in marine physiology at the University of South Florida, aims to shed light on this event and further analyzes the responses of different animals to ocean warming.
tea paper, entitled “Unique thermal sensitivity imposes an energetic cold-water barrier for vertical hikers” was published in nature climate change.
Responses to climate change
“The basic narrative for the last few years has been that as the ocean warms and loses oxygen, the animals that live in it will be driven out of their natural habitat and migrate to cooler waters at more northerly latitudes,” Seibel said. “But that’s an oversimplification.”
Marine animals will not react immediately to climate change.
The study examined the relationship between oxygen, temperature and the metabolic demands of vertical migrants. This includes billions of marine animals, from tiny crustaceans called krill to giant squid. Seibel and his co-author Matt Birk, Seibel’s former graduate student and professor at Saint Francis University in Pennsylvania, used models to understand how six species of krill and the jumbo squid would respond metabolically to different parameters that are day and night approach night habitats.
“Vertical wanderers reject the basic narrative, which is largely based on studies of coastal animals,” Seibel said.
As the oceans continue to warm, vertical migrants that live in tropical zones, like squid, are likely to expand their range northward. This does not mean that they will necessarily leave their native tropical zones.
Seibel argued that this probably happened 20 years ago, when jumbo squid appeared in record numbers off the California coast. Back then, instead of climate change causing the migration, an El Nino event temporarily brought warmer water to the coast. This can be viewed as a short-lived climate model.
The warmer water allowed the squid to expand their range north where they could exploit new food sources, although food was plentiful in the tropical regions.
“It wasn’t that they didn’t have enough oxygen or that it was too hot for them further south; Before the El Nino event, it was too cold for them in the north,” said Seibel. This nuance is important and is related to their metabolic requirements.
Vertical migrants versus coastal species
Coastal species experience a fairly constant supply of oxygen in waters that are well mixed with the atmosphere compared to vertical migrants that live at depth during the day. At depth it is cold and dark and there is less oxygen. Vertical migrants travel to the relatively warm sea surface at night to feed, where oxygen is plentiful and foraging is safer.
“This study is a good example that the conclusions we often draw from well-studied and easy-to-understand organisms may not apply to the greater biodiversity and lifestyle in the oceans,” Birk said.
The researchers concluded that the metabolic rate of vertical migrants is four to five times more affected by temperature than that of most coastal species. For example, when the squid are at depth they don’t do much at all, but when they move to shallower waters to eat their metabolic rate increases significantly.
By incorporating the increased effects of temperature on the vertical migrants’ metabolic rates into their models, the researchers determined that climate change will expand the vertical migrants’ available habitat by that much north and south than ten to twenty degrees of latitude by the end of the century.
“We really need to look at animal physiology and better understand how different species evolve and adapt to environmental conditions,” Seibel said.
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